Tasks Checklist has a limit on the size of file attachments, each file can be not larger than 30MB.
If you need to attach larger files to a checklist item, here's how to do it:
- Open your OneDrive tab in MS Teams and upload your file there (you can just drag-and-drop it from your desktop)
Click Share or simply Copy the Link to the intended file

Paste it to the Tasks Checklist item description

- That's it, your colleagues will be able to access the files via the link directly from the checklist
Make sure to check the access settings of the file, so it is available to your team members.
